Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade
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Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade

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Nb sputtered 150 MHz quarter-wave resonators for ANU LINAC Upgrade (Nikolai Lobanov - 20')
Speaker: Nikolai Lobanov - The Australian National University | Duration: 20 min.

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Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade Presentation Transcript

  • Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade
    • Pb-Sn technology
    • Multi-stub resonators update
    • Choice of Nb-coated QWRs
    • Other thin films srf applications
    October 2010 Nikolai Lobanov Nuclear Physics, RSPE, ANU
  • October 2010
  • Largest scale application of sc in Australia October 2010
  • Module cryostat with 3 SLRs October 2010
  • October 2010 Phase Diagram of Superconductors Ginzburg-Landau Parameter k GL =  L /  0 : k GL <0.71 Type I k GL >0.71 Type II  nucleate fluxoide ~10 -6 s » T rf ~10 -9 s so s/c persists up to H sh >H c H sh  0.89H c / k GL 0.5 for k GL « 1 H sh  1.2H c for k GL  1 H sh  0.75H c for k GL » 1 Phase diagram from Yogi Thesis 1977
  • Properties of Superconductors October 2010 Lattices from cst-www.nrl.navy.mil/lattice/struk Material Pb Pb96 % Sn4% Nb (bulk) Nb (film) Nb 3 Sn YBCO MgB 2 (dirty) T c , K 7.2 9.2 18.2 90 39  /kT c 2.1 1.86 2.25  L(o) , nm  ( 20C150MHz ) ,  28 18.7 36 15.6 65 200 a-b 1000 c 140  0 , nm 111 64 6 1.5 6 l (0) , nm Mean free path 1000 90 30 1.0 k GL 0.5-2 ~1 3-12 20 100 H c1 , Oe - 1700 200 H c (term) , Oe 800 2000 5350 H c2 , Oe - 2400 22000 >100 T 24500 H SH , Oe 1000 2400 4000 Lattice FCC Sn:BCT BCC
  • Low field surface resistance: Pb, Nb, Nb 3 Sn October 2010 In RF shielding of E field by supercurrent is incomplete due to inertia of e - so normal e - interact with E-field dissipating energy (two-fluid model by London) RF surface resistance based on Bardeen Cooper Schrieffer (BCS) theory: R BCS =A (  L ,  0 ,v F , l ) T -1 f  exp(-  (T) /kT)+R 0 ,  2, R 0 - residual resistance R BCS calculated from Halbritter program R BCS =0.89x10 -4 T -1 f 2 exp(-17.67/T) R BCS =0.94x10 -4 T -1 f 2 exp(-39.6/T) R BCS =0.69x10 -4 T -1 f 1.9 exp(-15.1/T) Pb98%Sn2% NIM PR A284(1989) 294 Nb Padamsee RFS for Acclerators 1998 p88 Nb 3 Sn Padamsee Supercond.Sci.Tech.14 (2001)R39
  • October 2010 Low field BCS & Residual Resistance: Pb Delayen 3 rd SRF Yogi Thesis high frequency: R s is dominated by R BCS at T >2.5 K low frequency: R s is dominated by R res at T=1.8-4.3 K R (T) =R BCS +R RES  117 n 
  • October 2010 High-field Performance: low  Nb and Nb/Cu Bulk Nb cavities M Kelly RFSC Limits 160 MHz 11% Nb/Cu ALPI QWRs:  =29  R BCS =70-145 n  Porcellato 12 th SRF
  • October 2010 High H -field Performance: Pb Yogi Thesis Test with sample in the middle of Helical s/c Nb coil low E-field Below H tr : loss due to week s/c links in grain boundaries Above H tr : loss due to H-field enhancement by sharp edges As thin as possible!
  • Pb-Sn Plating SLRs at ANU: Problems Low melting point metals like Pb and Sn take a long time to solidify and the corresponding surface diffusion distance becomes long resulting in formation of large grains. October 2010 At some plating condition a dendrite can be generated.
  • High E,H - fields Performance: Pb (cont) October 2010
    • Mechanical polishing of pre-plated 1 µ PbSn surface
    • Reverse pulse plating high quality 0.3 µ PbSn cosmetic layer over it
    H tr =370 Oe Plating Pb96%-Sn4% at ANU, R SURF  130 n  at 6 W H tr =262 Oe Delayen 3 rd SRF+2005 discussion @ Jefferson Curve E: decreased FE and increased other loss mechanisms
  • Pb-Sn Plating SLRs: Results October 2010 This procedure has proven to be successful in re-plating 12 ANU SLRs including 4 resonators with cracks in electron-beam weld.
  • Substrate preparation October 2010 tumbling degreasing
  • Superconductor coating laboratory October 2010 high pressure rinsing GN 2 drying PbSn plating
  • Clean room facilities class ~500 October 2010 assembling SLR and module cryostat
  • Characterization of sc films October 2010
  • Intermodulation distortion technique for SLRs October 2010
  • Twin stub resonator status I October 2010
  • Twin stub resonator status II October 2010
    • Cold test delayed due to vacuum failure
    • Doughnuts geometry is
    • to be changed to suppress
    • multipackting
  • October 2010 Pushing the Limits of SRF Pb For SLR H p /E acc = 105 Oe/MV/m leading to E acc =5 MV/m (limited by H c ) and E acc =6.1 MV/m (limited by H sh ) For Pb at 4.3 K H c =H (0) (1-(T/T c ) 2 )= 530 Oe and H sh =1.2H c =636 Oe Data for PbSn alloys is not available, the best ANU SLR operates at E acc =3.9 MV/m limited by FE
    • Plating final layer ~0.1  at over-potential (higher current density)
    • Plating multi-layers of Pb and PbSn alloys
    • Vacuum annealing or melting crystalline Pb film to make it amorphous
    • High power and helium processing on-line at 1kW peak RF power
    • RF gasket conditioning (PbSn pre-plating of lead wire)
    • Fundamental SRF properties of Pb, PbSn films shall be further investigated
    • ANY MORE IDEAS?
    Pushing the Limits of Pb:
  • October 2010 Nb/Cu SRF & TF Technology Common features: Base Pressure <10 -8 Torr; Bias Substrate –60  -100 V; Substrate temperature 100-500 C°. Challenges: Complex Geometry and Hydrides in bulk-like films Magnetron CERN, ACCEL, Cornell, ANU DC Cathode INFN Legnaro ECR *) JLAB Vacuum Arc *) , INFN A.Soltan HPPM *) , CERN Laser Ablation, JLAB Dep. Rate  /hour 0.5-6 0.5 1.5 2-3 10 6-72 RRR 5-10 10 20-100 20-100 - -
  • Latest developments
    • EIF Funds available over the next 4 years to upgrade Linac with 4-8 resonators: Nb-coated QWRs ? Collaborators are welcome
    • Another EIF project is Re-buncher @1.2 MV/m. Can we make it of MgB2 or HTS?
    • What about sc (HTS) phase detector installed in the Linac cryostat?
    • ACAS collaboration between ANU, UM, ANSTO and AS has been launched on 13 th July 2010 http://epp.physics.unimelb.edu.au/ACAS
    October 2010
    • Thank you !
    October 2010